In recent years demand for piezo-ceramic actuators or, in short, piezo actuators has risen sharply owing to their increased use, for example in the latest diesel injection systems produced by the automobile industry. This demand has also encouraged development work on piezo actuators. In several new fuel-injection or injector designs the piezo actuators are completely surrounded by diesel fuel. This type of injection system is described as “wet design”.
As the piezo actuators are chemically and electrically attacked in direct contact with diesel fuel which contains impurities or which has been modified with additives, a protective envelope has to be provided for the piezo actuator. The protective envelope should provide electrical insulation against a possible short circuit caused by the electrically conductive fuel as well as chemical insulation against attack by the surrounding fuel on the components of the piezo actuator.
In the state of the art metal housings of various designs are known which surround the piezo actuator. One example of such a metal housing is a corrugated tube. The metal housings are filled with suitable liquid filler materials to effect a transfer of the pressure applied by the fuel on the piezo actuator located inside, but this type of design has the disadvantages that it is expensive to manufacture and takes up a lot of space.